Apply button is greyed out in subdivision modifier how to fixe this?
I managed to solve the issue by selecting the object on which I have to apply sub div modifier, then I &quot;make the single user object and data&quot;.

The problem was that I had created a Duplicated Linked object Alt + D instead of a Duplicate Object Shift + D.
For those who does not know the difference between Duplicated Linked Object Alt + D and Duplicate Object Shift D below is the explanation:

The  duplicate linked  Alt +D works as an instance. Meaning it creates the instance copy of the original model, and if I make changes on one model it will affect both.

The duplicate object Shift + D makes a complete separate copy of the object. Meaning that any changes to it will not affect the original model, as it is a completely as separate object.